Yo-yos have provided countless hours of entertainment to children and adults alike for many years. Generally speaking, yo-yos comprise two matching disc-shaped components oriented in a mirror-image arrangement and fixed in relation to one another on a central axle. A string, which functions as a tether, is mounted on and winds around the central axle as the yo-yo is released and retracted. Many yo-yo design features have been adopted over the years to confer different performance properties.
Among the desirable features of a high performance yo-yo is that it spin freely at the end of its string for as long a time as possible before the spin action ceases, this feature being referred to as "sleeping." Many yo-yo tricks incorporate maneuvers that are performed while the yo-yo is sleeping. Early yo-yos were assembled with one end of the string captured between the axle and one side of the yo-yo. Such yo-yos cannot spin, or sleep, at the end of the string and therefore cannot perform a majority of the known yo-yo tricks, specifically those that require the yo-yo to sleep. More recently, many yo-yos have used a detachable string looped around the axle and leading from the axle to the player's hand. Using this technique, the yo-yo is left free to spin or "sleep" for a time, thus allowing the user to perform certain tricks.
A sleeping yo-yo must be "waked," or caused to engage the string at the axle, to initiate rewinding of the string. Capstan friction, which occurs between the portion of the string looped around the axle and the peripheral surface of the rotating axle, is required to initiate the rewinding of the string. Capstan friction between the string and the axle, necessary to wake the yo-yo, also acts to limit spin and playability. If the friction is reduced sufficiently to produce long spin time, some other provision must be made to permit the yo-yo to be returned to the player. The trade-offs between long spin, which requires low capstan friction and waking, or retraction, which requires a certain level of capstan friction to initiate the return, have generally required compromises in the design and playability of the yo-yo.
U.S. Pat. No. 3,175,326 discloses a yo-yo incorporating an anti-friction bearing fixed on the central shaft, which is fixed on the disc components. This bearing yo-yo has a long spin time, but requires the string to become wedged in a wedge ring or between the bearing and the disc to return the yo-yo to the user's hand. This provides uncertain and unpredictable return characteristics. Lodging of the string in a groove or wedge ring also tends to chafe the string and produce uneven windings that may result in uneven yo-yo travel and reduces string life. Moreover, because the central shaft and the bearing ere fixed, the yo-yo cannot be disassembled. The bearing cannot be cleaned or lubricated, and the string cannot be safely replaced.
U.S. Pat. No. 3,805,443 discloses a yo-yo design in which the side caps are removable and maximum weight is distributed in the outer periphery of the yo-yo body. Distribution of greater than 80% of each yo-yo body in the outer annular portion produces a flywheel effect and provides longer spin times that are desirable for performing tricks. The yo-yo also features a spool mounted on the central axle to reinforce the thin-walled central areas of the yo-yo bodies.
Yo-Yos having the capability of being dismantled and reassembled are known. U.S. Pat. No. 4,207,701 discloses a yo-yo in which the center axle, including a string guide, is removable and replaceable. This feature is important when hardwood axles are used to lend the desired "feel" of the classic yo-yo and the "sleeping" characteristics. Hardwood tends to become polished by repeated contact with the string, which reduces capstan friction and thus reduces the playability of the yo-yo. This patent also discloses an arrangement whereby either of the two body portions may be oriented in either of two orientations. Depending on the configuration of the body portions, several yo-yo configurations are possible.
U.S. Pat. No. 4,332,102 discloses a yo-yo in which the string is attached to a solid pulley bearing mounted on the central shaft. The patent observes that placing a solid plastic bearing between the yo-yo string and the central shaft increases the spin time of the yo-yo. This design incorporates centrifugal clutch mechanisms mounted in the body portions and engaging the sides of the bearing pulley to engage the gearing pulley as the yo-yo's rotational rate slows and thus provide retrieval of the yo-yo. The centrifugal clutches are only effective to retrieve the yo-yo, however, and they add significantly to the cost and mechanical complexity of the yo-yo. Moreover, yo-yos having a clutch mechanism generally have limited capability to perform many tricks, because the clutch diminishes the length of spin time and may engage sooner than desired during the performance of tricks.
U.S. Pat. No. 4,895,547 discloses a yo-yo in which a low friction solid polymeric spool is rotatably mounted on the central axle so that the axle rotates freely within the spool. The spool may be formed from a polymeric material having good lubricity properties, such as acetal. In practice, lubricant must be applied regularly to the axle to maintain the necessary frictional characteristics of the axle and the spool that permit retrieval of the yo-yo. When the lubricant wears off, there is insufficient friction to properly return the yo-yo to the player. The spool preferably has a circumferential groove for receiving the string. This patent also discloses the use of radially extending ribs surrounding the axle sockets in a starburst pattern. The ribs enhance the ability of the yo-yo to engage the string when retrieving, or waking the yo-yo.
U.S. Pat. No. 5,100,361 recognizes that the deliberate reduction or elimination of capstan friction has resulted in the need for some other interaction between the string at the axle and the rotating parts of the yo-yo to initiate rewinding of the string. The '361 patent discloses a yo-yo having an axle bearing in which the gap between the two yo-yo halves is adjustable to vary the amount of friction and therefore vary the performance properties of the yo-yo. The adjustability of this yo-yo to provide different performance properties for different levels of players is beneficial primarily for advanced players. Less skilled players would have difficulty adjusting the yo-yo to provide performance capabilities suitable for their skill level.
As is evident from the review of prior art patents, many yo-yo designs have been proposed with the objective of long spin time. Long spin times have been achieved, but the use of long spinning yo-yos is generally confined to experts and often the reduced friction at the axle makes return of the yo-yo more difficult for less experienced users. Complex and expensive mechanisms, such as centrifugal clutches, have been incorporated to provide a yo-yo having a relatively long spin time that can be returned to the player and played by a less experienced player or novice. There remains a need in the art for a yo-yo that has a simple mechanical design, that can be easily and inexpensively maintained, and that exhibits long spinning characteristics which permit the user to perform tricks, yet is returnable to the user easily with a simple flick of the wrist.
Low friction axle ball bearings have been incorporated in long-spinning yo-yos. To applicants' knowledge, all of the axle ball bearings incorporated in yo-yos to date have included races constructed from metallic materials such as steel. High precision metallic bearings comprising a plurality of metallic balls retained in precisely machined inner and outer metallic races have been used to provide the required low friction characteristics. High precision metallic bearings generally require use of lubricants, which may necessitate cleaning and maintenance, and which may affect the performance of the yo-yo under different temperature and humidity conditions. Such metallic axle bearings tend to corrode over time, and also contribute substantially and detrimentally both to the weight at the center of the yo-yo and to the cost of the yo-yo.